Nanoscopic lipid domain dynamics revealed by atomic force microscopy.

Area of Science:

• Membrane Biophysics
• Lipid Bilayer Systems
• Surface Science

Background:

• Intrinsic heterogeneities, such as domain formations, are crucial for biological membrane structure and function.
• Understanding lipid domain behavior is key to deciphering complex membrane processes.

Purpose of the Study:

• To investigate domain formation in mixed lipid bilayers composed of DPPC, DLPC, and cholesterol using atomic force microscopy (AFM).
• To characterize the coexistence of microscopic and nanoscopic domains and their dependence on lipid and cholesterol concentrations.
• To elucidate the influence of substrate support on lipid phase behavior compared to free-vesicle systems.

Main Methods:

• Atomic Force Microscopy (AFM) for high-resolution imaging of lipid bilayers.
• Confocal light microscopy for studying giant unilamellar vesicles (GUVs).
• Phase balance analyses to compare domain behavior in supported membranes versus free vesicles.

Main Results:

• Coexistence of microscopic and nanoscopic domains observed at room temperature.
• DPPC-rich domains were approximately 1.4 nm higher than DLPC-rich areas due to phase differences.
• Domain size varied with DPPC and cholesterol concentrations, with fragmentation and fusion observed at specific cholesterol levels.
• Significant differences in phase behavior were noted between supported membranes and free-vesicle systems.

Conclusions:

• Solid substrate support influences lipid phase behavior in membrane systems.
• A new 3D phase diagram is proposed to illustrate substrate effects on lipid phase phenomena.
• Findings provide insights into membrane heterogeneity relevant to biological systems.